1. To test our first hypothesis, we measured blood pressure (BP) and plasma MBG in young (3-mo old) and aged (24-mo old) Sprague-Dawley rats, and in aged rats determined the effect of immunoneutralization of MBG on the expression of pro-fibrotic genes in left ventricular (LV) myocardium. One week following a single administration to aged rats of an anti-MBG monoclonal antibody (n=6) or vehicle (n=6), the expression of genes and levels of proteins implicated in pro-fibrotic signaling were assessed in LV myocardium by qPCR analysis. BP did not change, and plasma MBG levels were elevated two-fold (P<0.05) in aged vs. young rats, and was accompanied by upregulation of genes implicated in TGF-signaling: TGF1 - 3-fold; CTGF1 - 6-fold; SMAD3 - 2-fold; collagen-1 - 2.6-fold. Expression of these genes was significantly suppressed following immunoneutralization of MBG in aged rats, although their expression remained higher than in young controls. The expression of a nuclear transcription factor Fli-1, a negative regulator of collagen-1 synthesis, was reduced by 3-fold in aged vs. young rats, and anti-MBG antibody restored levels of Fli-1 in aged rats to the level in young controls. Thus, the age-associated increase in MBG participates in pro-fibrotic signaling linked to advancing age, and cross-talk between TGF-dependent and Fli-1-dependent pro-fibrotic pathways, underlies this MBG effect. 2. To test the second hypothesis, we measured blood pressure (BP), PWV, plasma MBG, and erythrocyte NKA in seven middle-age control subjects and in eight age-matching RH patients treated with lisinopril / amlodipine / hydrochlorothiazide (LAH), before and after addition of spironolactone (50 mg/day) to the LAH regimen for six months. Prior to the addition of spironolactone to the LAH regimen, plasma MBG, BP, and PWV were higher, and NKA activity was reduced in RH patients vs. controls (Table). Addition of spironolactone to conventional triple (LAH) therapy for RH reduced BP and PWV, and reversed erythrocyte NKA inhibition in the absence of an effect on plasma MBG. Thus, aldosterone antagonists reversed MBG-induced NKA inhibition and reduced PWV and BP in patients with RH. These beneficial effects of aldosterone antagonists may, in part, be linked to a concomitant reduction in arterial fibrosis. Table: ------------------------------------------------------------------------------------------ .............................Controls..........RH baseline........RH after spironolactone treatment ------------------------------------------------------------------------------------------ Age (years).................50+/-3..............55 +/- 2...............55 +/- 2 Plasma MBG (nmol/L)......................0.24+/-0.03.......0.42+/-0.07*.........0.53 +/- 0.05** Erythrocyte NKA (micromolPi/mL/hr).......2.8 +/- 0.2........1.9 +/- 0.2**.........2.3 +/- 0.2 # PWV (m/sec)...............6.3 +/- 0.6........8.9 +/- 0.3**.........8.4 +/- 0.2 # 24-hour SBP (mmHg).......................125 +/- 2..........149 +/- 3**...........142 +/- 2 # 24-hour DBP (mmHg).......................75 +/- 2.............95 +/- 2**..............86 +/- 2 # ------------------------------------------------------------------------------------------- Mean+/- SE; *-P<0.05;**-P<0.01 vs. controls, # -P<0.01 vs. baseline RH (ANOVA)